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Impact of Clinical Off-Centering On Organ Dose and the Effects of Using An Automatic Centering Technology

I Barreto1*, R Lamoureux2 , C Carranza1 , N Quails1 , N Correa1 , L Rill1 , M Arreola1 , (1) University of Florida, Gainesville, FL, (2) University of New Mexico Hospital, Albuquerque, NM


(Wednesday, 8/1/2018) 10:15 AM - 12:15 PM

Room: Room 207

Purpose: To determine the effect of patient off-centering on organ doses in computed tomography (CT) and evaluate the impact of an automatic centering technology.

Methods: With IRB approval, clinical off-centering was measured in 300 patients examined with chest-abdomen-pelvis CT. Four cadavers were scanned on a 320-slice CT scanner, with the table shifted in 1-cm increments for a vertical range of 8 cm and lateral range of 4 cm. Optically stimulated luminescent dosimeters were placed within organs, and organ doses were measured at each table position. Regression models of organ dose were produced as a function of centering error. Methods were repeated using a commercially-available automatic centering technology that compensates for off-centering by modifying the tube current output.

Results: Off-centering was observed in 88% of patients in the vertical direction (average 1.4 cm, maximum 5.4 cm), and in 80% of patients in the lateral direction (average 0.7 cm, maximum 5.2 cm). When shifted vertically, the scanogram experienced magnification, making the patient appear smaller when positioned posteriorly and larger when positioned anteriorly, causing significant differences in tube current values (P<0.005). Correlations were observed between the degree of vertical miscentering and the percentage difference in dose from the central position for the lung, colon, uterus, ovaries, and skin with the difference ranging from -46% to 22% (P<0.005). Automatic centering technology aimed to normalize the dose output with an inverted trend with table height. The percentage difference ranged from -17% to 20%, resulting in smaller dose differences compared to methods without compensation.

Conclusion: Miscentering occurs frequently in the clinic, with patient position having a strong correlation on optimal system output and patient dose. Automatic centering technology has the potential to reduce these differences to deliver tube current values closer to those delivered at the central position for achieving consistent image quality and patient dose.

Funding Support, Disclosures, and Conflict of Interest: This work was conducted with financial support from Toshiba America Systems in the form of a research grant.


Not Applicable / None Entered.


Not Applicable / None Entered.

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